Method of making pure magnesium oxide



Feb. 17, 1942. s. B. HEATH, ETAL r 2,273707 METHOD OF MAKING PUREMAGNESIUM OXIDE Filed Oct. 30, 1939 &

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I M e ATTORNEYS Patented Feb; 17, 1942 UNITED'STTES PATENT OFFICESheldon B. Heath and Alvin Dahl, Midam, Mich., assignors to The DowChemical Company, Midland, Mich., a corporation ot Michigan ApplicationOctober 30, 1939, Serial No. 3o;s94

` (Cl. 23 2o`) 4 Claims.

The inventionlrelates to a method of producing magnesium oxide of, highpurity. It mor e particularly concerns a method of producing highly puremagnesium oxide from metal-li@ magnesium and water or steam.

In one of the uses of magnesium oxide, as wherein it isto' be used asanelectrical insulator and heat conductor for an electric resistancewire heating element in stoves or the like, it is desirable and inmostinstances necessary that it be of high purity, for otherwise itselectrical conductivity is suflciently high to reduce the effici'ency of.the heating elements to the extent that they are impractical -forcommercial use. For example, wherein' magnesium oxide is used as anelectric insulator and heat conductor, it has been found desirable thatthe alkalies should `be entirely absent or present only in spectroscopic traces, iron should not be present in an amount substantiallyabove-0.05 per cent,- aluminum oxide and' calcium oxide should not bepresent in amounts substantially'abdve 0.05 and 0.5 'per cent,respectively while silicon oxide should not be present in an amountsubstantially above 2.0'per cent.

It is, therefore, the principal object of the invention to provide amethod of making magnesium oxide of a' purity such that its electricalconductivity is of a Very low value.

Another object of the invention is to provide a method of producingmagnesium' oxide of high purity from metallic magnesium, and steam owater. I

Still other objects andadvantages will be apparent as the description ofthe invention proceeds.

We have discovered that by subjecting mea tallic magnesium to the actionof steam'or wa-` ter at high temperature in a container made of suitablematerial out of the presenceof air or other gases which react with themagnesium,

particularly carbon dioxide and nitrogen, while controlling the Volumeof steam or water coming into contact with' the magnesium metal, the

temperature and rate of reaction between the.

- -tion, such mode illustrating, however, but one of the various ways inwhich the invention may be carried into efiect.

In the drawing, the single figure is a diagrammatic View in verticalsectionof a drum-type reactor adapted to be rotated in a fumace setting.i

As shown, reactor l, surrounded by furnace 2, is pr'ovided at one' endwith a shaft 3 rigidly attached to the end of the reactor at 4 so thatas the shaft 3 is rotated on supporting bearings 5 and '6 the reactor isalso caused to turn about its axis. The other end of the drum reactor isprovided with a central opening 1, through which sleeve 8, dependingfrom the furnace wall, extends into the reactor I. The opening 'I isprovided of such a diameter that there will be clearance between thesleeve and the end of the drum as 'is rotated about the sleeve 8. Awater or steam'line 9, suitably controlled by valve o, extends into thereactor through the sleeve 8 and serves as a means whereby water orsteam, as thecase may be, may be introduced into the reactor. Athermo-couple well I l also extends into the reactor through the sleeve8 and acts as a receiver for a thermo-'couple which serves to indicatethe temperature interiorly of the reactor.

derstood from the following description wherein a charge of metallicmagnesium is reacted with steam and converted to magnesium oxide.Reactor I is charged with a suitable amount of magnesium metal and heatis applied to the reactor as shaft 3 is caused to rotate. Thetemperature of the reactor is gradually increased, but, before reactiontemperature is reached, a quantity of water or steam is introducedthereinto through water or steam line 9 to sweep any air from thereaction chamber. The introduction of steam or water is continued and.as the temperature of the reactor reaches about 650 C., the meltingpoint of magnesium metal, the reaction between`the magnesium and thesteam rapidly begins. The introduction of water is continued at such arate as to maintain thetemperature of the reactor between about 650 and'800 C. considerable care must be exercised as regards .the rate ofintroduction of water or steam into The reactor l` is also provided witha door |2, held in place as by means of clamping bolts I 3, which servesas a means whereby the presence of the magnesium since the reactionbetween molten magnesium and steam is of a violent nature. As thereaction continues, the hydrogen produced is swept from the reactorthrough the opening around the sleeve 8 and burns upon coming incontact-with air. The burning hydrogen is forced through the opening atconsiderable pressure and thus 'acts to exclude air from the reactor.After about 2 /2 hours, depending however on the amount of magnesiumbeing reacted, the rate of introduction and amount of water or steamintroduced, and

the temperature of the reaction, the evolution of hydrogen through theopening will cease, indicating that the reaction is complete. After theevolution of hydrogen has ceased the introduction of steam or water isstopped and heat applied to keep the .temperature of the reactorsubstantially above 650 C. for approximately /2 hour in order to insurethat any magnesium hydroxide formed will be converted into magnesiumoxide. The reactor may then be allowed to cool, after which the productmay be withdrawn therefrom.

The rate of reaction and the temperature of the reaction can becontrolled by controlling the rate at which the steam or water isintroduced into the reactor. Since a large amount of heat is given oi asthe steam reacts with the metallic magnesium, the temperature of thereaction can be raised by'increasing the rate of introduction of thesteam or water or lowered by decreasing the' rate of introduction of thewater. The water employed should be relatively pure in order that a pureproduct will be obtained. Distilled water that has been recentlyrboiling' todrive off gases dissolved therein capa- `ble of affectingthe purity of the product is preferably employed. In generaL aconsiderable excess of water is employed over the theoretical out themethod should be at least as high a purity as that desired in theproduct. However, we have found that the ordinary magnesium of commerceis usually satisfactory and gives a product of suitable purity. Themetal may be used in any suitable form such as rods, billets,

ingots, powder, or the like.

The reactor or container in which the reaction is carried out should bemade of, or at least linedwith, a metal that does not scale or otherwiseliberate materials that contaminate the product at the temperature ofthe reaction.

For example, reactors made of or lined with a stainless steel, such asone containing 18 per cent chromium and 8 per cent nickel, or one madeof or lined with nickel or inconel, may be suitably used withoutcontaminating the product.

During the reacton the reactor should be rotated so that the magnesiumoxide or hydroxide that first forms is scraped or broken away from thesurface of the metal exposing fresh metal to the action of the steam. Ina drum reactor, such as that above described, a peripheral speed of from2 to 6 inches, and preferably 4 inches, per minute has 'been found to bemost Satisfacto'ry.

While a rotating reactor is preferably employed because of the ease ofcontrolllng the temperature and rate of reaction, a stationary reactormay be employed and superheated steam introduced of such a temperaturethat -additional heat need not be supplied to bring about reaction. If astationary reactor is to be employed, it may be suitably lined with arefractory such as magnesia in suitable form.

In the foregoing manner, magnesium metal may be converted into magnesiumoxide of high purity such that it may be suitablyemployed as anelectrical insulator and heat conductor for electrical resistance wireheating elements or the like, or even as a Chemical reagent.

1. In a method of producing highly pure magnesium oxide from metallicmagnesium and water, the steps which comprise adding water to a body ofmolten magnesium in an enclosed space in the absence of air and atsubstantially atmospheric pressure, controlling the rate of addition of-the water so that the temperature of the reaction does not exceed about800 C., stopping the addition of water when'the evolution of hydrogensubstantially ceases, and thereafter heating the reaction mixture aboveabout 650 C.

2. In a method of producing highlyapure magnesium oxide from metallicmagnesium and water, the steps which comprise adding substantially purewater to a body of molten magnesium in the absence of air and atsubstantiallyatmospheric pressure, controlling the addition of water sothat the temperature of the reaction is between 651 to 800 C., stoppingthe addition of water when the evolution of hydrogen substantiallyceases, and thereafter heating the reaction mixture above about 650 C..

3. In a method according to claim 1 in which the water is supplied tothe reaction in the form of steam; 4 i

4. In a method according to claim 1 in which the water is supplied tothe reaction in the form of superheated steam and the subsequent heatingoperation carried out after the evolution of hydrogen ceases isconducted above about 750 C. v

SHELDON B. HEATH.

ALVIN D. DAHL.

